The overall objective of the AFC4Hydro research project is to design, implement and validate in full-scale water turbine an active flow control system that permit to increase efficiency and reduce the dynamics loads on the structure at any off-design operating conditions and during transient operations. Specifically, the system will modify the draft tube flow field to mitigate or supress the pressure fluctuations induced by the vortical flow which limits the operation of actual hydraulic machines. Special attention will be given to the flow instability leading to the formation of the vortex rope in the draft tube.
A combination of two innovativ technologies will be used in the draft tube: (1) injection of pulsating momentum (IPM) with a specific frequency, amplitude and phase by means of actuators; (2) injection of continuous momentum (ICM) in the form of water jets with controlled speed and orientation directed against the swirling flow. The IPM handles the problem at its source, while the ICM is the remedy when the problem arises. A structural health monitoring (SHM) system will be developed to continuously evaluate the performance of the turbine in real time and used as a feedback to adjust the flow control strategy with a specifically designed Controller. This closed loop configuration will permit to enhance the stability of the flow and decrease the level of unsteadiness also during transients such as ramp up and ramp down.